1. Field of the Invention
The present invention relates to a liquid crystal light valve which is used for a projection type display device, a spatial light modulating element and a coherent light operating element.
2. Description of the Related Art
The inventors of the present invention know of other addressing systems for forming an image on a liquid crystal valve according to a signal standing for an image (referred to as an image signal) which include an electric addressing system, a laser head addressing system or a light addressing system.
As to the electric addressing system, a liquid crystal light valve of a simple multiplexing driving system is arranged to have a plurality of scanning electrodes and signal electrodes formed in a matrix manner. This liquid crystal light valve is arranged to selectively apply an electric voltage on any of the pixels consisting of scanning electrodes X1, X2, . . . Xn and signal electrodes Y1, Y2, . . . Ym ranged in the X direction and the Y direction, respectively and transmit a scanning signal and a data signal through electric wires.
As to the light addressing system, a liquid crystal light valve is arranged so that a liquid crystal layer and a photoconductive layer are laid between both of the glass substrates and provide transparent electrodes for directly addressing the liquid crystal through the effect of irradiated light.
Typical examples of the light addressing type liquid crystal light valve have been disclosed in J. Grinberg, A. Jacobson, W. Bleha, L. Miller, L. Frasss, D. Boswell and G. Myer "A New Real-time Noncoherent To Coherent Write Image Converter" and "The Hybrid Field Effect Liquid Crystal Light Valve", Optical Engineering Volume 14, 217 (1975).
In these examples, the liquid crystal light valve of a light addressing type is arranged to have a pair of glass substrates, two transparent electrodes, a photoconductive layer, a dielectric mirror, two orientation films, a sealing member, a liquid crystal layer, and an A. C. power source. The A. C. power source serves to apply a voltage between the transparent electrodes. When an addressing (writing) ray of light is incident to one glass substrate, the impedance of the photoconductive layer is made smaller on the light-hit area (bright state) so that the voltage is applied from the A. C. power source to the liquid crystal layer. On the other hand, on the other area where no light impinges (dark state), the impedance of the photoconductive layer is kept constant so that no voltage may be applied to the liquid crystal layer.
The difference between the bright state and the dark state leads to forming an image data corresponding to the addressing light. The image data is allowed to be read by a reading ray of light.
This type of liquid crystal light valve may apply to a projection type display device, a coherent operating element, and so forth.
As another example, there has been proposed an addressing type liquid crystal light valve having a combination of the electric addressing system and the light addressing system. As disclosed in Japanese Lying Open No. 2-134617, a data signal in the electric addressing system is allowed to be transmitted by using a light signal.
The above-described electric addressing system liquid crystal light valve of a simple multiplex driving type is arranged to apply divided voltages on the pixels except display pixels. This known light valve hence has a disadvantage of lowering a display contrast. The time when a data signal used for controlling a display state is applied to the display pixels is a constant time defined by a duty ratio. For the remaining time, the data signal having no concern with the control of the display state is applied onto the display pixels. Hence, the liquid crystal disadvantageously responds to the data signal sent at a non-selecting time. To overcome these disadvantages, a method referred to as a voltage averaging method is generally used for the simple multiplex driving system having matrix electrodes.
However, the margin of an operating voltage in the voltage averaging method is made lower as the number n of scanning electrodes is increasing. In a case that the used liquid crystal material has constant electro-optical characteristics, the number n of scanning electrodes for holding a practical display quality is defined. Hence, the use of the voltage averaging method disadvantageously makes it possible to provide a higher resolution or a larger screen than that arranged for the held scanning electrodes.
Further, in the known electric addressing type liquid crystal valve, the resistance of wire and the capacitance cause a signal waveform to be delayed, resulting in being unable to realize a large device or a high-density device.
On the other hand, the known liquid crystal light valve of a light addressing system needs a CRT or an addressing light source such as a liquid crystal panel. This brings about a disadvantage that the overall device cannot be made reduced in size.
In the addressing system having a combination of the known electric addressing system and the known light radiation addressing system (see Japanese Lying Open No. 2-134617), the waveform of the data signal is converted into the change of light intensity and is written on the photoconductive layer. Hence, disadvantageously, it is necessary to provide a higher sensitive photoconductive layer which will be sensitive to a minute change of light intensity. And, the photoconductive layer has to have a quite uniform sensitivity distribution for uniformly displaying an image on the screen.